Databases. Five databases OULU-NPU [1]} (denoted as O), SiW [2]} (denoted as S), CASIA-FASD [3]} (denoted as C), Replay-Attack [4]} (denoted as I), MSU-MFSD [5]} (denoted as M) are used in the testing protocols. OULU-NPU and SiW are large-scale high-resolution databases containing four and three protocols to validate the generalization (e.g., unseen environment and spoof mediums) of models, respectively, which are utilized for intra-dataset testing. CASIA-MFSD, Replay-Attack, and MSU-MFSD are databases that contain low-resolution videos with much fewer video clips and are used for cross-dataset testing to validate the generalization ability to testing data with large distribution shift. There are three capture devices with quality ranging from low to high in CASIA-FASD, two devices in SiW and MSU-MFSD, and only one device in the other datasets. The fine-grained class number and the other statistics of databases are shown in Tab. REF . Note that in Oulu-NPU, even the collections are captured by six different types of phones, the quality and fine details are pretty similar, so we only split the patch type into five classes in total. More details and sample images can be found in the supplementary material.
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